The drive train of a conventional motor vehicle with an internal combustion engine as the sole drive source usually has a starting component in the power flow between the drive source and the drive wheels in order to enable a startup process of the motor vehicle. Hydrodynamic torque converters or friction clutches are examples of such a starting component. The drive train of a motor vehicle with an electric motor as the sole drive source does not usually require a starting component, since the electric motor can accelerate the vehicle from a standstill.
If a startup process is to occur solely with the assistance of the internal combustion engine, the drive train of a parallel hybrid vehicle typically requires a starting component. Various alternatives for starting a motor vehicle with a parallel hybrid drive train by electrical components are known from the prior art. For example, the patent application DE 10 2006 018 058 A1 of the applicant discloses various types of startup procedures for a motor vehicle with a parallel hybrid drive train. FIG. 4 of the said prior art shows the variations over time of a purely electrically powered startup operation with a slipping converter bridging clutch; FIG. 5 shows the same with the converter bridging clutch engaged.
Both of the aforementioned startup procedures have advantages and disadvantages. A startup operation without a slipping starting component is particularly energy efficient, since none of the energy generated by the drive source is lost during the slip operation between the drive source and the drive wheels as lost power. However, at low transmission speeds, as is the case during the startup operation, a pump, which is mechanically driven by the transmission and which is provided for supplying pressure to the hydraulic consumers of the transmission, generates only a small volumetric rate of flow. This feature can restrict the functionality of the transmission and, as a result, can lead to a degradation of the driving comfort, for example, due to the slipping, gear-forming shift elements.
Even a stopping operation without a slipping starting component may be advantageous, since during a startup operation immediately following the stopping operation, the slipping starting component does not have to first be engaged or bridged again in order to enable a startup that is as energy efficient as possible.